Retrieval of the Diffuse Attenuation Coefficient from GOCI Images Using the 2SeaColor Model: A Case Study in the Yangtze Estuary
Abstract:
Validation with radiometric data from field observations shows that the 2SeaColor model generates best estimates of Kd for the full range of observations, with the largest determination coefficient (R2 = 0.935) and the smallest root mean square error (RMSE = 0.078 m-1). Specifically, the Zhang model and the Lee model provide better estimation for clear water where Kd (490) < 0.2, while results from 2SeaColor is rather comparable. As for turbid water where Kd (490) > 0.2 m-1, 2SeaColor model is verified more appropriate with RMSE of 0.186m-1, compared to RMSE of 0.279 m-1 and 0.256 m-1 for the Zhang model and the Lee model, respectively.
The 2SeaColor model is last applied on the GOCI (Geostationary Ocean Color Imager) level 2 product (L2P) to produce Kd maps over the Yangtze estuary, resulting in a reasonable distribution and expected range of Kd as Kd (490) varying from 0.04 to 9.82 m-1 for the image acquired at 02:16 UTC, March 8 of 2013.
The analytical 2SeaColor model is able to provide consistently stable and accurate Kd estimates in both clear and turbid waters without the need of tuning empirical coefficients from field measurements, and thus has great potential for estimating Kd over optically complex waters.